Radiant energy transducers find a wide range of applications in modern technology. Electrically driven transducers, for example, emit radiation to illuminate a desired area or footprint. The transducer system may illuminate the area for a number of reasons. For example, if the emitting transducer emits visible light, the illumination may facilitate use of the area by human personnel. If the illumination of the area provides infrared radiant energy, the illumination may facilitate some associated detection operation or human monitoring of the area through special night vision equipment.
Other radiant energy transducers detect radiant energy from within a desired field of view and provide signals for further electrical processing. For example, a light detecting transducer may provide signals that a processor can analyze to determine the direction and/or intensity of incoming light. The processed information may represent a position of a reflective object or light source within the field of view. These are just a few examples of the applications of radiant energy transducer systems.
Different applications of radiant energy transducers require different transducer performance characteristics. For example, an illumination application might require that the transducer uniformly illuminate a flat surface of a specified area (the footprint) at a known distance from the transducer with a specified radiation intensity. Typically, the specification for such an illuminating transducer would not specify the amount of radiation transmitted to areas outside the specified footprint. Simple radiation sources, such as light bulbs or lights with reflectors and/or lenses typically distribute a substantial amount of radiation outside the desired footprint. This reduces efficiency. Stated another way, to achieve the desired illumination intensity within the footprint, the power applied to the transducer must be relatively large in order to allow for the energy lost to areas outside the desired footprint. Also, they often over radiate a portion of the desired footprint.
Similar problem arise in radiant energy detecting transducers. To insure adequate sensitivity to energy from within the field of view, the transducer typically will receive additional radiant energy from outside the desired field of view. Also, it often is difficult to maintain uniform sensitivity over the entire field of view.
Prior attempts to address these problems have involved complex arrangements of lenses and reflectors. Such arrangements make transducer manufacture expensive. Such arrangements also are subject to problems of misalignment and raise concerns about the durability and ruggedness, in applications outside of laboratory conditions.
A need therefore exists for radiant energy transducer systems, e.g. emitters and detectors, having high efficiency and desired operational characteristics for specific applications. The transducer systems should be relatively easy to manufacture and therefore relatively inexpensive. Also, there is a need for transducers of this type which are relatively rugged and durable, when used in real applications.
Constructive Occlusion
Applicants have developed a number of radiant energy transducer systems, which reduce some of the above noted problems, based on a theory of beneficial masking referred to as `Constructive Occlusion`. Constructed Occlusion type transducer systems utilize an electrical/optical transducer optically coupled to an active area of the system. The systems utilize diffusely reflective surfaces, such that the active area exhibits a substantially Lambertian characteristic. The active area typically comprises a diffusely reflective cavity. A mask occludes a portion of the active area of the system, e.g. the aperture of the cavity, in such a manner as to achieve a desired response characteristic for the system.
For example, in a series of prior related cases, applicants disclosed cavity and mask based transducer systems which provide uniform response characteristics (e.g. emission energy for light distributors or sensitivity for detectors) over a wide range of angles relative to the transducer system. The prior Constructive Occlusion cases include application Ser. Nos. 08/589,104, 08/589,105 and 08/590,290 filed on Jan. 23, 1996 and application Ser. No. 08/836,811 filed on May 21, 1997, the disclosures of which are incorporated entirely herein by reference.
Applicants' prior Constructive Occlusion type transducer systems have allowed considerable tailoring of the optical/electrical performance characteristics of radiant energy transducing systems. However, some desired applications require still further enhancements to achieve the desired system characteristics, and a need still exists to further increase the efficiency of the transducer systems. For example, a need still exists for a transducer system of even higher efficiency exhibiting uniform performance over a designated planar surface.